1. Field of Invention
This invention is generally directed to toner and developer compositions that can be used in hybrid jumping development systems, including, but not limited to, magnetic image character recognition systems.
2. Description of Related Art
There are many known electrostatographic processes for recording an image, wherein an electrostatic latent image is formed on a charge retentive surface, such as a photoreceptor, developed with toner, and transferred to a recording medium, such as paper. The toner-based image is generally fixed to the recording medium by any suitable process, such as heating, applying pressure, treating with a solvent vapor, or a combination thereof.
Toners, and developers comprising the toners, used in electrostatographic processes have well-known, standard compositions. For example, in a type of electrostatographic system known as hybrid jumping development (HJD), the developer is generally a standard, two-component conductive developer comprising standard toner particles that adhere to triboelectrically-charged carrier particles.
In HJD systems, the toner particles are loaded onto a donor roll (or development roll) and a “toner cloud” is formed when the toner particles are transported to the development zone (or “development nip”) formed by a charge retentive surface and the donor roll. Transportation to the development zone is powered by applying alternating potentials to the donor role from two development fields (potentials across an air gap), such that the toner particles “jump” from the donor roll to the charge retentive surface. In other words, the toner particles are sufficiently attracted to the electrostatic latent image on the charge retentive surface, such that they disassociate from the carrier particles to form the toner-based image. The resulting toner-based image is then transferred from the charge retentive surface to any suitable recording medium and optionally heated to permanently affix the toner-based image to the recording medium. A description of hybrid jumping development systems is set forth in U.S. Pat. No. 5,890,042, for example, incorporated by reference herein in its entirety.
Regarding the two development fields in HJD systems, generally, the first field, the A/C jumping field used for the toner cloud generation, has a typical potential of about 2.6 k volts peak to peak at about 3.25 kHz frequency, for example, and the second field, the D/C development field, is used to control the amount of developed toner mass on the charge retentive surface.
Although standard HJD systems and other known, standard systems, use standard toner and developer, in specialized electrostatographic processes, including specialized HJD-based processes and other specialized processes, standard toners and developers do not function effectively due to the highly specific needs of the specialized process. A specific example of such a specialized process is the process used in the magnetic image character recognition (MICR) imaging and printing system, which relies on a high speed reading and sorting process to print checks and other financial documents. MICR systems must maintain consistent signal strength, uniformity from document to document, and image permanence in high-speed readers/sorters. To meet at least these requirements, MICR systems employ conductive developers comprising magnetically readable toner.
Although magnetic toners in general are known, they suffer from serious disadvantages. For example, magnetic toners contain a heavy loading of ferromagnetic particles, such as, for example, iron oxide or other magnetic material, which is needed to produce the requisite magnetic signal strength. However, toners having a heavy loading of iron oxide are difficult to manufacture since an adequate dispersion of the iron oxide particles in the toner resin, for example, is hard to achieve and then maintain once achieved. Furthermore, due to decreased fusing efficiencies resulting from the heavy magnetic loading, the image quality obtained with known magnetic toners is low compared to the image quality obtained with standard toners in non-MICR processes.
Thus, it would be desirable to provide magnetic toner compositions that have the benefits of non-magnetic toners, such as, for example, image quality and ease of production, yet have the capability of use in HJD-based systems and MICR systems. In other words, it would be desirable to provide electrostatographic toners that produce high quality images and can be used in standard banking reader/sorter equipment, i.e., MICR equipment.
Moreover, it would be desirable to provide highly conductive developer compositions capable of use in HJD-based systems and MICR systems.